[RIO DE JANEIRO] The Brazilian Amazon is increasingly being cleared to grow crops rather than for grazing cattle, making the process even more harmful to the environment, say researchers.

Over the course of a three-year study led by Ruth DeFries of the University of Maryland in the United States, clearing for cropland accounted for nearly one fifth of deforestation in one state of the Brazilian Amazon.

The results are published this week by Proceedings of the National Academy of Sciences.

Using deforestation maps, field surveys and satellite data to follow what happened to large pieces of land cleared of rainforest in the state of Mato Grosso, the team found that an area over one third the size of Jordan — about 36,000 square kilometres — was cleared between 2001 and 2004 for large-scale mechanised agriculture.

They say this contradicts previous claims that Brazil's expanding crop production is met by converting land previously cleared for cattle ranching.

Their findings define a "new paradigm of forest loss in Amazonia", although cattle pasture still remains the dominant land use, say the researchers.

Mato Grosso is one of the nine states of the Brazilian Amazon, and was home to 87 per cent of the increase in Brazilian cropland from 2001 to 2004 and 40 per cent of new deforestation.

DeFries says that clearings for cropland are in general larger than clearings for pasture, and more of the biomass in those areas is removed.

"We didn't quantify the amount of remaining biomass in the paper, but we suggest that carbon emissions per area will be greater when more biomass is removed," she told SciDev.Net.

Amazon deforestation is Brazil's largest source of carbon dioxide emissions.

Flávio Montiel, director of environmental protection at the Brazilian Institute of Environment and Renewable Natural Resources (Ibama) told SciDev.Net that the government is monitoring new research into deforestation, and investing in new technologies, such as those used in the study, to detect deforestation in real time.